Hardhat ZKit

The ultimate TypeScript environment for Circom development.

What

This hardhat plugin is a zero-config, one-stop Circom development environment that streamlines circuits management and lets you focus on the important - code.

- Developer-oriented abstractions that simplify r1cs, witness, zkey, and vkey generation processes.
- Support of groth16 and plonk proving systems.
- Recompilation and resetup of only the modified circuits.
- Full TypeScript typization of signals and ZK proofs.
- Automatic downloads of phase-1 ptau files.
- Convenient phase-2 contributions to zkey files.
- Practical witness (with signals substitution) and proof testing via chai assertions.
- Invisible platform-specific and wasm-based Circom compiler management.
- Simplified node_modules libraries resolution.
- Rich plugin configuration.
- And much more!

Installation

``bash
npm install --save-dev @solarity/hardhat-zkit
`

And add the following line to your hardhat.config:

`ts
import "@solarity/hardhat-zkit"; // TypeScript

require("@solarity/hardhat-zkit"); // JavaScript
`

> [!TIP]
> There is no need to download the Circom compiler separately. The plugin automatically installs required compilers under the hood.

Usage

The hardhat-zkit is a zero-config plugin, however, you may add the following to your hardhat.config file:

`ts
module.exports = {
zkit: {
compilerVersion: "2.1.9",
circuitsDir: "circuits",
compilationSettings: {
artifactsDir: "zkit/artifacts",
onlyFiles: [],
skipFiles: [],
c: false,
json: false,
optimization: "O1",
},
setupSettings: {
contributionSettings: {
provingSystem: "groth16", // or "plonk"
contributions: 2,
},
onlyFiles: [],
skipFiles: [],
ptauDir: undefined,
ptauDownload: true,
},
verifiersSettings: {
verifiersDir: "contracts/verifiers",
verifiersType: "sol", // or "vy"
},
typesDir: "generated-types/zkit",
typesWitnessLimit: 50000,
quiet: false,
},
};
`

Where:

- compilerVersion - The value to indicate which Circom compiler to use (latest by default).
- circuitsDir - The directory where to look for the circuits.
- compilationSettings
- artifactsDir - The directory where to save the circuits artifacts (r1cs, zkey, etc).
- onlyFiles - The list of directories (or files) to be considered for the compilation.
- skipFiles - The list of directories (or files) to be excluded from the compilation.
- c - The flag to generate the c-based witness generator (generates wasm by default).
- json - The flag to output the constraints in json format.
- optimization - The flag to set the level of constraint simplification during compilation ("O0", "O1" or "O2").
- setupSettings
- contributionSettings
- provingSystem - The option to indicate which proving system to use ("groth16", "plonk" or ["groth16", "plonk"]).
- contributions - The number of phase-2 zkey contributions to make if groth16 is chosen.
- onlyFiles - The list of directories (or files) to be considered for the setup phase.
- skipFiles - The list of directories (or files) to be excluded from the setup phase.
- ptauDir - The directory where to look for the ptau files. $HOME/.zkit/ptau/ by default.
- ptauDownload - The flag to allow automatic download of required ptau files.
- verifiersSettings
- verifiersDir - The directory where to generate the Solidity | Vyper verifiers.
- verifiersType - The option ("sol" or "vy") to indicate which language to use for verifiers generation.
- typesDir - The directory where to save the generated typed circuits wrappers.
- typesWitnessLimit - The maximum number of witness substitution signals to generate types for.
- quiet - The flag indicating whether to suppress the output.

$3

There are several hardhat tasks in the zkit scope that the plugin provides:

- compile task that compiles or recompiles the modified circuits with the main component.
- setup task that generates or regenerates zkey and vkey for the previously compiled circuits.
- make task that executes both compile and setup for convenience.
- verifiers task that generates Solidity | Vyper verifiers for all the previously setup circuits.
- clean task that cleans up the generated artifacts, types, etc.

To view the available options, run the help command:

`bash
npx hardhat help zkit
`

$3

The plugin provides full TypeScript typization of Circom circuits leveraging zktype library. Both groth16 and plonk proving systems are supported.

The following config may be added to tsconfig.json file to allow for a better development experience:

`json
{
"compilerOptions": {
"paths": {
"@zkit": ["./generated-types/zkit"]
}
}
}
`

$3

In order to utilize user-friendly Chai assertions for witness and ZK proof testing, the chai-zkit package needs to be installed:

`bash
npm install --save-dev @solarity/chai-zkit
`

And add the following line to your hardhat.config:

`ts
import "@solarity/chai-zkit"; // TypeScript

require("@solarity/chai-zkit"); // JavaScript
`

The package extends expect chai assertion to recognize typed zktype objects for frictionless testing experience.

The plugin supports:

1. Basic witness input -> output testing.
2. Deep witness (signals) substitution testing.
3. Proof generation success/failure testing.
4. Circuit constraints number testing.

> [!NOTE]
> Please note that for witness testing purposes it is sufficient to compile circuits just with zkit compile task, without generating the keys.

$3

The plugin extends the hardhat environment with the zkit object that allows typed circuits to be used in scripts and tests:

To see the plugin in action, place the Multiplier circuit in the circuits directory and execute:

`bash
npx hardhat zkit make
`

This command will install the newest compatible Circom compiler, compile the provided circuit, download the necessary ptau file regarding the number of circuit's constraints and the proving system of choice, build the required zkey and vkey files, and generate TypeScript object wrappers to enable full typization of signals and ZK proofs.

Afterward, copy the provided script to the test directory and run the tests via npx hardhat test. You will see that all the tests are passing!

> [!TIP]
> Check out the Medium blog post and Solarity circom-lib to learn more.

$3

---

- async getCircuit(, ) -> zkit

The method accepts the name of the main component of the circuit, optional proving system and returns the instantiated zkit object pointing to that circuit.

The method works regardless of how the circuit was compiled, however, if zkit compile task was used, the zkit methods that utilize proof generation or proof verification would throw an error by design.

In case there are conflicts between circuit file names and main component names, you should use the fullCircuitName, which has the following form: circuitSourceName:circuitName.

Where:

- circuitSourceName - Path to the circuit file from the project root.
- circuitName - Circuit main component name.

The optional provingSystem parameter should only be specified if multiple proving systems were set in the config. Otherwise, leave it as undefined.

> [!IMPORTANT]
> Please note that the method actually returns the zktype typed zkit wrapper objects which enable full TypeScript typization of signals and proofs. Also, check out the zkit documentation to understand zkit object capabilities and how to interact with circuits.

Future work

- [x] ZK proofs generation with custom witness files (witness substitution).
- [ ] Per-circuit plugin configuration.
- [ ] BLS12-381 on-chain ZK verifiers (EIP-2537).
- [ ] Support for --prime bls12381 Circom (and Snarkjs) compilation flag.

Known limitations

- Currently there is minimal support for var Circom variables. Some circuits may not work if you are using complex var-dependent expressions.
- Even though the plugin provides support of Circom v2.2.2, its newest feature bus is not supported.
- Due to current wasm` memory limitations (address space is 32-bit), the plugin may fail to compile especially large circuits on some platforms.